Osteoarthritis (OA), also called osteoarthrosis or degenerative joint disease (DJD), is the most common form of chronic disorder of synovial joints. It is characterised by progressively degenerative changes in the articular cartilages over the years, particularly in weight-bearing joints.

Types of Osteoarthitis

Primary OA

Primary OA occurs in the elderly, more commonly in women than in men .he condition may be regarded as a reward of longevity. Probably, wear and tear with repeated minor trauma, heredity, obesity, aging per se, all contribute to focal degenerative changes in the articular cartilage of the joints.

Genetic factors favouring susceptibility to develop OA have been observed; genetic mutations in proteins which regulate the cartilage growth have been identified e.g. FRZB gene

Secondary OA

Secondary OA may appear at any age and is the result of any previous wear and tear phenomena involving the joint such as previous injury, fracture, inflammation, loose bodies and congenital dislocation of the hip.

Morphological features

The weight-bearing joints such as hips, knee and vertebrae are most commonly involved but interphalangeal joints of fingers may also be affected. The pathologic changes occur in the articular cartilages, adjacent bones and synovium .

1. Articular cartilages

• The regressive changes are most marked in the weight-bearing regions of articular cartilages.
• There is loss of cartilaginous matrix (proteoglycans) resulting in progressive loss of normal metachromasia.
• This is followed by focal loss of chondrocytes, and at other places, proliferation of
  chondrocytes forming clusters.

2. Bone.

• There is death of superficial osteocytes and increased osteoclastic activity causing rarefaction, microcyst formation and occasionally microfractures of the subjacent bone.
• The margins of the joints respond to cartilage damage by osteophyte or spur formation.

3. Synovium.

• There are no pathologic changes in the synovium but in advanced cases there is low-grade chronic synovitis and villous hypertrophy.
• There may be some amount of synovial effusion associated with chronic synovitis

Symptoms

• Joint stiffness,
• Diminished
  mobility
• Discomfort and pain
• The symptoms are more prominent on waking up from bed in the morning.
• The interphalangeal joints lead to hard bony and painless enlargements in the form of nodules at the base of terminal phalanx called Heberden’s nodes